Artificial limbs, including leg prostheses, employ a wide range of technologies to provide solutions suitable to many differing needs. For a trans-femoral amputee, basic needs in a leg prosthesis include stability, while standing and during the stance phase of a walking gait, and mechanical compatibility with the walking (or running) gait and some manner of knee flexion during stance and swing phases of a gait.
Certain trade-offs exist between stability, and walking or running performance. A simple, non-articulable leg (having no movable knee), for example, may provide maximum stability, but does not provide for an ideal gait. Also, sitting may be awkward if a person cannot bend their knee.
For people having lost their biological knees, it is important that the prosthetic joint functions properly and is reliable. There are numerous types of prosthetic joint designs available, each having its benefits and shortcomings.
A widely used prosthetic joint design is of a single axis type. The single axis knee employs a simple hinge at the level of the anatomical knee. Such a simple design results in low cost, light weight, and durability. However, little gait assistance is provided to the amputee by the limb itself; the amputee is required to expend a certain degree of muscle power to help to control and stabilize the prosthetic leg.
The single axis knee may be configured with a fluid control unit to increase or decrease the swing phase resistance as one speeds up and slows down. Yet by adding the fluid control unit, the cost of the knee and complexity of the knee are greatly increased.
In accordance with another type of prosthetic joint, a polycentric knee design employs a mechanically complex plurality of hinge or rotation points that allow variations in the action of the knee through the gait, typically providing increased stability early in the stance phase while allowing easy bending during the swing phase and while sitting. Additional mechanical complexity is often found in the form of air or hydraulic cylinders that vary swing phase resistance or flexion during variations in the gait, or provide for shock absorption. Microprocessor controllers may be employed to measure aspects of the gait to control operation of the air or hydraulic cylinders or other components of the knee.
Of course, because of the complexity of the polycentric knee design, this design is not as reliable as the single hinge design. Moreover, this design costs substantially more to produce than the single hinge design due to its additional moving parts.
Other highly complex mechanical (and in some cases microprocessor controlled) prosthetic joints have evolved to improve the performance of leg prostheses. Current prosthetic joints are often a complicated system including joints, arms, bearings, cylinders, and other mechanical and electromechanical components. Further, some employ sophisticated electronics including microprocessor circuits and instrumentation of the various parts of the knee.
The complexity of such prosthetic joints tends to adversely affect the potential life of the knee as well as security to the user, as the parts are subject to wear. Moreover, with increased mechanical and electronic complexity comes the need for increased maintenance and tuning to achieve or maintain proper function.
It is therefore desirable to provide a prosthetic joint that provides improved functionality, user security, and performance in a simplified structure having few moving parts, and that can be produced at low cost.